1. Field of the Invention
This invention relates generally to a communications handset and, more particularly, to a multiformat auto-handoff communications handset to support communications and handoffs between multiple signal formats at multiple carrier frequencies.
2. Discussion of the Related Art
Mobile and cellular communication systems currently utilize several types of signal formats and carrier frequencies. For example, some of the various cellular standards used today include AMPS (Analog Modulation Phone Service), IS-54 (North American Digital Cellular), PCN (Personal Communications Network), DECT (European Digital Cordless Telephone Standard) and GSM (Groupe Speciale Mobile). These signal formats typically operate around 800 MHz to 900 MHz or around 1.70 GHz to 1.90 GHz and utilize a network of terrestrial base stations.
In addition, with the immense growth in the mobile and cellular communications industry, many new and planned signal formats and carrier frequencies will be utilized to increase the number of possible users and the service coverage areas. These new and planned signal formats include FDM (Frequency Division Multiplex), TDMA (Time Division Multiple Access), CDMA (Code Division Multiple Access) and many others. The new and planned signal formats will operate between 800 MHz to about 2.40 GHz and utilize both terrestrial base stations and satellite base stations.
Today, the currently utilized communications handsets (telephone) are each specifically designed to support a particular signal format and a particular carrier frequency. Therefore, each communications handset is quite limited in its capabilities to support multiple signal formats at multiple carrier frequencies. The current approaches to making the communications handsets more compatible with various signal formats and also various carrier frequencies is essentially to build multiple RF (radio frequency) hardware strings, such that each RF hardware string is capable of supporting a particular signal format at a particular carrier frequency. Another approach is to use add-on circuitry to convert the communications handset from one signal format to another or from one carrier frequency to another. Yet another extreme approach is to maintain multiple communications handsets so that when the user exits one service coverage area, the user would utilize another communications handset to initiate a new call in the particular service coverage area.
However, these current approaches are very poor and not cost effective since they easily double the RF hardware required and waste precious RF output power generated by the communications handset. This directly impacts on the size and the weight of the communications handset as well as the battery operating time. In addition, the multiple circuits and the add-on circuitry adds a significant additional cost to the communications handset.
What is needed then is a multiformat auto-handoff communications handset which is capable of: supporting multiple signal formats at multiple carrier frequencies; eliminating multiple RF hardware strings; operating over a broadband and extending the service coverage area by communicating over both terrestrial and satellite base stations. It is therefore an object of the present invention to provide such a device.